Cellulose pulp for esterification purposes and processing of same



Patented Jan. 28, 1936 2,028,846

UNITED STATES PATENT OFFICE CELLULOSE PULP FOR ESTERIFICATION PURPOSES AND PROCESSING OF SAME George A. Richter, Berlin, N. H., assignor to Brown Company, Berlin, N. 11., a'corporation oi Maine No Drawing. Application June 22, 1931, Serial No. 546,151

2 Claims. (01. 260100) The subject of this invention is a pulp for alized at lower temperatures with weaker soluviscose syrups and the like, as well as the processtions of caustic soda than those necessary at ing which the pulp undergoes in passing from higher temperatures. In fact, the liquor may be its original condition to the ultimate syrup or used at or below freezing temperatures, as dis- 5 generic product. In making viscose syrups, such closed in my application Serial No. 538,132, filed 5 as are spun into artificial silk, it is the practice to May 18, 1931. (now Patent No. 1,859,891, dated use soft-wood pulps as the cellulosic base, for such May 24, 1932), in which case, the liquor may, for pulps are convertible into syrups having the deinstance, be caustic soda solution of only 5% siredcharacteristics. It is practically impossistrength applied at, say, 0 0., together with the ble to realize satisfactory viscose syrups from desired amount of hypochlorite or other oxidant. 10

hardwood pulps, doubtless on account of the ex- So, too, the oxidant content of the solution may cesslve pentosans, resins, and other objectionable be varied, depending upon such factors as the non-alpha-cellulose components present in such particular oxidant used, the solution viscosity of pulps even when they have been prepared by the the pulp serving as the starting material, the

sulphite process of fiber liberation, which, as is temperature of treatment, etc. Because the oxi- 15 well lmown, is conducive to pulp's of comparatively dant is used with a large excess of. alkali, its tendlow pentosan content. Indeed, a sulphite pulp ency to degrade the pulp by causing the formaderived from hard woods of the character of birch, tion of Oxycelluloses is aimost entirely inhibitedbeech, and maple may have a pentosan content In contrast with the mercerizing action, the acranging from 5% to 7%, or even higher; yet, for tivity of the oxidant is greater at higher tempereconomical reasons, for instance the lower cost atures than at lower temperatures. Wherefore, to of hard woods, themuch higher yield of pulp per secure a given effect through the use of oxidant cord of wood, etc., the pulpmaker would like to at, say, room temperature (20 0.), it is necessary market a product derived from hard wood, such to use more oxidant than at below room temperaas birch, rather than one procured from soft ture, say, 10 C.

wood, such as spruce. As a specific example of procedure falling I have found that hardwood pulps, notably Within the purview of this present invention. I hard-wood sulphite pulp, may b d t fulfill may cite the following. I take a birch sulphite the requirements for xanthation and the like, if pulp. either in bleached o b ed condition such pulps are subjected to the action of a. merand aining, say, 5% to 7% pentosans, and mix 30 .cerizing liquor preferably in the presence of an a, Caustic Soda Solution of 0f oxidant, for a sufiicient period of time to remove strength at room temperature to pl'oduce Stock penbosans resins, andother nomalpha cehmoses, density of, say 5% to 10%. In some cases, the in such amount as to leave a fiber residuum having hrdwood P a be advantageously P etreated an alpha cellulose content of at least about 94% i Water, p l rite bleach liquor, 35 and a pentosan content of not greater than about or like and then Washed to remove some 05 1.5%. Aside from the purifying action exercised the hgneous f' other colmng matter which it by the liquor on the pulp serving as the starting would otherwise be necessary to eliminate as by material, the liquor functions simultaneously to the addition of bleach the mercerizing liquor 40 reduce the solution viscosity of. the fiber so dras- Wlth Whlch the Pulp 15 Subsequently treated- 40 tically that the mercerized fiber residuum, after some types? Pardwood pulp P to advantage washing, can be xanthated directly and completely t an lmtlal treatment WP weak acid without requiring the usual intermediate 1ong lution or other reagent to facilitate the procuretime ageing of the soda cellulose into which it is m 9 finished product, especially low t an f rmed as part of the xahthating process tion viscosity. The solution should preferably 45 The mercerizing liquur thus e f r two fii contain an oxidant in amount suflioient to reduce th pulp t t Same t and the pulp may the solution viscosity of the pulp to the desired be admixed with the mercerizing liquor in the Value While it is being dy. 1% to 10% same bulk condition as it was liberated in the hypochlorite bleach (either s dium or calcium ,pulp mill, as the handling of the fiowable pulp b 1' t0 P a si m perman anate. 50 suspension thus produced is easy, inexpensive, The oxidant also tends to remove residual ligneous and conducive to a uniform product. The merand coloring matter from the pulp, and thus to cerizing liquor may be of varying causticity, dewhiten it. Considerably less permanganate than pending upon the temperature at which it is used, hypoohlorite bleach need be used for bringing for, as is well known, mercerization can be reabout a given solution-viseosity-lowering eflect, 55

because of the greater activity of the permanganate on the fiber, especially under strongly alkaline conditions. After remaining suspended in the mercerizing liquor containing the oxidant for about 2 to 8 hours or more, the pulp is washed free from liquor. .The washed pulp, when tested, exhibits an alpha cellulose content of at least about 94% and a pentosan content not exceeding 1.5%. When insufllciently white, it may be postbleached to the desired whiteness under conditions to preserve its high alpha cellulose content.

a For instance, incase a raw or unbleached pulp has undergone processing as described but has not acquired the desired whiteness during mercerization, it may be ltreated, after washing, with a hypochlorite bleach liquor of sufllcient potency to ensure the desired whiteness of product. The bleach liquor should also contain suflicient free alkali, such as caustic soda, sodium carbonate, or the like, to maintain a condition of appreciable alkalinity tl'ierein throughout the bleaching operation, as the free "alkali preserves the previously-attained alpha cellulose content in the piilp.

The washed, and, if desired, post-bleached pulp is then converted into' 'viscose syrup substantially in the following manner. The pulp in sheet or other suitable form is treated with excess caustic soda solution of about 18% strengthgand is then squeezed to the caustic soda content necessary for combining with'the fiber as so called soda cellulose. The soda cellulose is then shredded, as usual, but rather than undergoing the conventional ageing under controlled temperature conditions for a considerable period of time, the shreds may be at once treated with carbon bisulphide in amount calculated to form viscose syrup. As already stated, the soda cellulose dissolves completely to form syrup of excellent clarity, color, and viscosity for spinning into silk and for fabrication into pelliclesor other viscose ultimates. 5

The hardwood pulp product of the present invention, while especially adapted for making xanthates or other esters, is by itself poorly adapted for papermaking: To begin with, it must be borne in mind that a hardwood pulp, since as birch sulphite pulp, is characterized by a much v shorter average fiber length than is spruce sulphite pulp; Mercerization further impairs the fiber for papermaking, because it destroys the abiiity of the fiber to become hydrated during xanthatiOn or other esterifying treatment, but

rather inures to its benefit, for its short fiber length means smaller units, which lend themselves to more uniform treatment with converting chemical and to a quicker conversion, and its mercerized state goes hand in hand with a better composition and lower solution viscosity. The

viscose syrups that are prepared from the special ly treated hardwood pulp product of the present invention have exceptional clarity and are very easily filtered,properties of great importance in the manufacture olf rayon.

My invention cq'mprehends the processing of various kinds of pre-liberated hardwood pulps, but it is more particularly aimed at such pulps which been pre-liberated by the sulphite process of 'eooking. The combination of the sulphite process of cooking the raw wood to produce pulp with the mercerizing step of the present invention makes possible an almost complete removal of the pentosans, which may be present to the extent of 20%, or even higher, in the raw wood, and which are highiy detrimental to the preparation of viscose syrups or other esters of usefulness, In li'eerating pulp from the raw hardwood by the sulphite process, one may use the typical acid sulphite cooking liquors containing sodium or calcium as the base and having 1% on more cpmbined 802 and 5% or more free $02. Theuse of anacid sulphite cooking liquor containing a large excess of free over combined S02 is of value, in that the acid sulphite cook itself removes most of the pentosans, and thus leaves less work to be done by the mercerizifig treatment of the present invention; The process of the present invention can be applied te alkaline-cooked hardwood pulpsfor instance, such pulps as are obtained by cooking hardwood chips in kraft or soda liquors. The pulps that are produced by such processes are higher in their pentosan content than sulphite pulp produced from the same wood. They are, therefore, even more diflicult to convert into a product suitable for viscose-making or the like, unless the process of the present invention is invoked. Thus, a kraft hardwood pulp mayi have a pentosan content ranging from 15% to 20%. Such a raw pulp, after a suitable pr'e-treatment with, say, 2% to 4% chlorine, based on pulp, in the form of chlorine water, followed by washing and treatment with a mercerizing liquor containing a suitable amount of hypochlorite bleach or its equivalent as hereinbefore described, yields a product that responds to xanthation or other esterifying reaction very nicely.

The main treatment of the pulpwith mercerizing liquor may advantageously be carried out in two steps, especially when the liquor contains an oxidant; Thus, the pulp may be brought into' suspension in the liquor at room temperature 20 C.); or higher to promote the reaction of 1 the oxidant on the pulpfland thus to facilitate the procurement of a final product pf low solution viscosity, whereupon the suspension may be cooled to room temperature (20 C.)

or to below room temperature to enhance its s olubilizing effect on the pentosans and thus to make possiblethe production of a final product of maximum alpha cellulose content. The cooling of the pulp suspension is preierabLv effected after the oxidant has been substantially consumed. To instance this sort of procedure, I may cite the admixture pf a pulp with a heated 15% caustic soda solution containing about 8% hypochlorite bleach, based on the weight of pulp, to produce a pulp suspension at, say, 40

C., whereafter, with thebleach practically consumed by reaction on the pulp, the suspension may be cooled tc:20 C. or lower and kept thereat for the desired period of time.

What I claim is:

l. A process which comprises suspending preliberated hardweod pulp in a mercerizing liquor containing an oxidant for about two to eight; hours or more, washing the mercerized pulp free. from n ercerizingliquor, treating the washed; pulp caustic soda to form soda cellulose,; and treating the soda cellulose without ageing with carbon bisulphide to form viscose. l

2. A'washed, mercerized hardwood pulp hav ing an alpha cellulose content of at least about 94%, a pentosan content not exceeding about 15%, and a solution viscosity suflicientls' low to permit such pulp to be converted directly into cellulose xanthate and without intermediate ageing of the soda cellulose prepared therefrom, said pulp being further characterized by an average fiber length much shorter than that of spruce sulphite pulp and the quicker convertibility of its shorter fiber units into cellulose xanthate and said pulp being prepared according to a process which comprises suspending preliberated hardwood pulp in a mercerizing liquor containing an oxidant for about two to eight hours or more and washing the mercerized pulp free 45 from mercerizing liquor.

' GEORGE A. RICHTER. 

